Optical device with reduced chromatic aberration and display device including the same

ABSTRACT

An optical device includes a first backlight configured to output first light of a first wavelength through a first output coupler, a first lens disposed to face the first output coupler and having a focal length with respect to the first light, a second backlight including a second output coupler, the second backlight being configured to output second light of a second wavelength through the second output coupler, a second lens disposed to face the second output coupler and having different focal lengths with respect to the first light and the second light, a third backlight including a third output coupler, the third backlight being configured to output third light of a third wavelength through the third output coupler, and a third lens disposed to face the third output coupler and having different focal lengths with respect to the first light, the second light, and the third light.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Korean Patent Application No.10-2020-0045237, filed on Apr. 14, 2020 in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND 1. Field

Example embodiments of the present disclosure relate to optical deviceswith reduced chromatic aberration and display devices including thesame.

2. Description of Related Art

Recently, holographic three-dimensional (3D) image display methods,which provide full parallax and are capable of making the depthperceived by the brain consistent with the focus of the eyes, have beengradually put to practical use.

According to such holographic display techniques, when light is radiatedonto a hologram pattern having recorded thereon an interference patternobtained by interference between reference light and object lightreflected from an original object, the light is diffracted and an imageof the original object is reproduced. When a currently commercializedholographic display technique is used, a computer-generated hologram(CGH), rather than a hologram pattern obtained by directly exposing anoriginal object to light, is provided as an electrical signal to aspatial light modulator. The spatial light modulator forms a hologrampattern and diffracts reference light from the light source according toan input CGH signal, thereby generating a 3D image.

In such a holographic display method, an optical element such as a fieldlens or a beam deflector may be used to display a holographic imageformed by a spatial light modulator at a predetermined position. Such anoptical element may be implemented based on diffraction. Diffractionelements have recently been used in many fields because diffractionelements may generate various optical effects and thin optical systemsthat may not be realized by using refractive elements of the relatedart. In addition, because such optical elements exhibit differentrefractive indices according to the wavelength of light, opticalelements are accompanied by chromatic aberration, and in particular,when diffraction-based elements are used to reduce the volume of theelements, the performance difference according to the wavelengthsfurther increases. Thus, there is a need for a method of preventing orreducing the chromatic aberration.

SUMMARY

One or more example embodiments provide optical devices with reducedchromatic aberration and display devices including the same.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of example embodiments of the disclosure.

According to an aspect of an example embodiment, there is provided anoptical device including a first backlight configured to output firstlight of a first wavelength through a first output coupler, a first lensdisposed to face the first output coupler and having a predeterminedfocal length with respect to the first light of the first wavelength, asecond backlight including a second output coupler disposed in parallelto the first output coupler, the second backlight being configured tooutput second light of a second wavelength through the second outputcoupler, a second lens disposed to face the second output coupler andhaving different focal lengths with respect to the first light of thefirst wavelength and the second light of the second wavelength, a thirdbacklight including a third output coupler disposed in parallel to thesecond output coupler, the third backlight being configured to outputthird light of a third wavelength through the third output coupler, anda third lens disposed to face the third output coupler and havingdifferent focal lengths with respect to the first light of the firstwavelength, the second light of the second wavelength, and the thirdlight of the third wavelength.

The first lens, the second lens, and the third lens may be geometricphase lenses.

When a focal length of the first lens with respect to the first light ofthe first wavelength is f1_1, focal lengths of the second lens withrespect to the first light of the first wavelength and the second lightof the second wavelength are f f2_1 and f2_2, respectively, and focallengths of the third lens with respect to the first light of the firstwavelength, the second light of the second wavelength, and the thirdlight of the third wavelength are f3_1, f3_2, and f3_3, respectively,EFL (f1_1, f2_1, and f3_1) that is a combination focal length of f1_1,f2_1, and f3_1 may satisfy the following condition: |f3_3−EFL(f1_1,f2_1, f3_1)|/f3_3<0.0005.

EFL(f2_2, f3_2) that is a combination focal length of f2_2 and f3_2 maysatisfy the following condition: |f3_3−EFL(f2_2, f3_2)|/f3_3<0.0005.

The first lens, the second lens, and the third lens may operate withrespect to light of a predetermined polarization, and the optical devicemay further include at least one phase retarder configured to causeincident light of the predetermined polarization to be incident on thefirst lens, the second lens, and the third lens.

According to another aspect of an example embodiment, there is providedan optical device including a first backlight configured to output firstlight of a first wavelength through a first output coupler, a first beamdeflector disposed to face the first output coupler and configured todeflect the first light of the first wavelength at a predeterminedangle, a second backlight including a second output coupler disposed inparallel to the first output coupler, the second backlight beingconfigured to output second light of a second wavelength through thesecond output coupler, a second beam deflector disposed to face thesecond output coupler and configured to deflect the first light of thefirst wavelength and the second light of the second wavelengthrespectively at different angles, a third backlight including a thirdoutput coupler disposed in parallel to the second output coupler, thethird backlight being configured to output third light of a thirdwavelength through the third output coupler, and a third beam deflectordisposed to face the third output coupler and configured to deflect thefirst light of the first wavelength, the second light of the secondwavelength, and the third light of the third wavelength respectively atdifferent angles.

The first beam deflector, the second beam deflector, and the third beamdeflector may be diffraction-based deflectors.

When an angle at which the first beam deflector deflects the first lightof the first wavelength is a1_1, angles at which the second beamdeflector deflects the first light of the first wavelength and thesecond light of the second wavelength are a2_1 and a2_2, respectively,and angles at which the third beam deflector deflects the first light ofthe first wavelength, the second light of the second wavelength, and thethird light of the third wavelength are a3_1, a3_2, and a3_3,respectively, EDA(a1_1, a2_1, a3_1) that is a combination deflectionangle of a1_1, a2_1, and a3_1 may satisfy the following condition:|a3_3−EDA(a1_1, a2_1, a3_1)|/a3_3<0.0005.

EDA(a2_2, a3_2) that is a combination deflection angle of a2_2 and a3_2may satisfy the following condition: |a3_3−EDA(a2_2, a3_2)|/a3_3<0.0005.

A display device may include the optical device, and a spatial lightmodulator configured to generate a hologram image by modulating thefirst light output from the first backlight, the second light outputfrom the second backlight, and third light output from the thirdbacklight.

The first backlight may include a first light source configured to emitthe first light of the first wavelength, and a first light guide plateincluding a first input coupler on which the first light from the firstlight source is incident and the first output coupler, the secondbacklight may include a second light source configured to emit thesecond light of the second wavelength, and a second light guide plateincluding a second input coupler on which the second light from thesecond light source is incident and the second output coupler, and thethird backlight may include a third light source configured to emit thethird light of the third wavelength, and a third light guide plateincluding a third input coupler on which the third light from the thirdlight source is incident and the third output coupler.

The first lens, the second lens, and the third lens may be geometricphase lenses.

When a focal length of the first lens with respect to the first light ofthe first wavelength is f1_1, focal lengths of the second lens withrespect to the first light of the first wavelength and the second lightof the second wavelength are f f2_1 and f2_2, respectively, and focallengths of the third lens with respect to the first light of the firstwavelength, the second light of the second wavelength, and the thirdlight of the third wavelength are f3_1, f3_2, and f3_3, respectively,EFL (f1_1, f2_1, and f3_1) that is a combination focal length of f1_1,f2_1, and f3_1 may satisfy the following condition: |f3_3−EFL(f1_1,f2_1, f3_1)|/f3_3<0.0005.

EFL(f2_2, f3_2) that is a combination focal length of f2_2 and f3_2 maysatisfy the following condition: |f3_3−EFL(f2_2, f3_2)|/f3_3<0.0005.

The display device may further include a beam deflector configured toadjust a position of a hologram image generated by the spatial lightmodulator.

The display device may further include a first beam deflector disposedbetween the first output coupler and the second output coupler andconfigured to deflect the first light of the first wavelength at apredetermined angle, a second beam deflector disposed between the secondoutput coupler and the third output coupler and configured to deflectthe first light of the first wavelength and the second light of thesecond wavelength respectively at different angles, and a third beamdeflector disposed such that the first light, the second light, and thethird light output from the third output coupler is incident on thethird beam deflector, the third beam deflector being configured todeflect the first light of the first wavelength, the second light of thesecond wavelength, and the third light of the third wavelengthrespectively at different angles.

The first beam deflector, the second beam deflector, and the third beamdeflector may be diffraction-based deflectors.

When an angle at which the first beam deflector deflects the first lightof the first wavelength is a1_1, angles at which the second beamdeflector deflects the first light of the first wavelength and thesecond light of the second wavelength are a2_1 and a2_2, respectively,and angles at which the third beam deflector deflects the first light ofthe first wavelength, the second light of the second wavelength, and thethird light of the third wavelength are a3_1, a3_2, and a3_3,respectively, EDA(a1_1, a2_1, a3_1) that is a combination deflectionangle of a1_1, a2_1, and a3_1 may satisfy the following condition:|a3_3−EDA(a1_1, a2_1, a3_1)|/a3_3<0.0005.

EDA(a2_2, a3_2) that is a combination deflection angle of a2_2 and a3_2may satisfy the following condition: |a3_3−EDA(a2_2, a3_2)|/a3_3<0.0005.

The first beam deflector, the second beam deflector, and the third beamdeflector may be electrically controlled to adjust a direction in whichincident light is deflected.

The display device may further include an eye tracking sensor, whereinthe first beam deflector, the second beam deflector, and the third beamdeflector may be controlled based on a signal sensed by the eye trackingsensor.

A display device may include the optical device and a spatial lightmodulator configured to generate a hologram image by modulating thefirst light of the first wavelength output from the first backlight, thesecond light of the second wavelength output from second backlight, andthe third light of the third wavelength output from the third backlight,and a field lens configured to focus the hologram image generated by thespatial light modulator at a predetermined position.

The first beam deflector, the second beam deflector, and the third beamdeflector may be electrically controlled to adjust a direction in whichincident light is deflected.

The display device may further include an eye tracking sensor, whereinthe first beam deflector, the second beam deflector, and the third beamdeflector may be controlled based on a signal sensed by the eye trackingsensor.

According to yet another aspect of an example embodiment, there isprovided an optical device including a first backlight including a firstlight source configured to emit a first light of a first wavelength anda first light guide plate that includes a first input coupler facing thefirst light source and a first output coupler, the first backlight beingconfigured to output the first light of the first wavelength through afirst output coupler, a first lens disposed to face the first outputcoupler and having a predetermined focal length with respect to thefirst light of the first wavelength, a second backlight including asecond light source configured to emit a second light of a secondwavelength and a second light guide plate that includes a second inputcoupler facing the second light source and a second output coupler, thesecond backlight being configured to output the second light of thesecond wavelength through a second output coupler, a second lensdisposed to face the second output coupler and having different focallengths with respect to the first light of the first wavelength and thesecond light of the second wavelength, a third backlight including athird light source configured to emit a third light of a thirdwavelength and a third light guide plate that includes a third inputcoupler facing the third light source and a third output coupler, thethird backlight being configured to output the third light of the thirdwavelength through a third output coupler, and a third lens disposed toface the third output coupler and having different focal lengths withrespect to the first light of the first wavelength, the second light ofthe second wavelength, and the third light of the third wavelength.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects, features, and advantages of certainexample embodiments of the disclosure will be more apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 illustrates a schematic configuration and an optical arrangementof an optical device according to an example embodiment;

FIG. 2 illustrates a conceptual focusing operation of a geometric phaselens that may be employed in the optical device of FIG. 1;

FIG. 3 illustrates a schematic configuration and optical arrangement ofan optical device according to another example embodiment;

FIG. 4 illustrates a schematic configuration and optical arrangement ofan optical device according to another example embodiment;

FIG. 5 illustrates a schematic configuration and optical arrangement ofan optical device according to another embodiment;

FIG. 6 illustrates an optical operation of a diffraction-based beamdeflector that may be employed in the optical device of FIG. 5;

FIG. 7 illustrates a schematic configuration and an optical arrangementof a display device according to an example embodiment;

FIG. 8 illustrates a schematic configuration and an optical arrangementof a display device according to another example embodiment;

FIG. 9 illustrates a schematic configuration and an optical arrangementof a display device according to another example embodiment;

FIG. 10 illustrates a schematic configuration and an optical arrangementof a display device according to another example embodiment;

FIG. 11 illustrates a schematic configuration and an optical arrangementof a display device according to another example embodiment; and

FIG. 12 illustrates a schematic configuration and an optical arrangementof a display device according to another example embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to example embodiments of which areillustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the exampleembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Accordingly, theexample embodiments are merely described below, by referring to thefigures, to explain aspects.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items. Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list. Forexample, the expression, “at least one of a, b, and c,” should beunderstood as including only a, only b, only c, both a and b, both a andc, both b and c, or all of a, b, and c.

Hereinafter, with reference to the accompanying drawings, exampleembodiments will be described in detail. The embodiments described beloware merely examples, and various modifications may be possible from theembodiments. Like reference numerals refer to like elements throughout,and in the drawings, sizes of elements may be exaggerated for clarityand convenience of explanation.

Hereinafter, an expression “above” or “on” may include not onlyimmediately on in a contact manner but also on in a non-contact manner.

Terms such as first and second may be used to describe various elements,but are used only for the purpose of distinguishing one element fromother elements. These terms do not limit differences in the material orstructure of the elements.

The expression of singularity in the present disclosure includes theexpression of plurality unless clearly specified otherwise in context.Also, terms such as “comprise” and/or “comprising” may be construed todenote an element, but may not be construed to exclude the existence ofor a possibility of addition of another element.

The term used in the embodiments such as “unit” or “module” indicates aunit for processing at least one function or operation, and may beimplemented in hardware, software, or in a combination of hardware andsoftware.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the disclosure are to be construed to cover boththe singular and the plural.

Also, operations of all methods described herein may be performed in anysuitable order unless otherwise indicated herein or otherwise clearlycontradicted by context. The use of any and all examples, or language(e.g., “such as”) provided herein, is intended merely to betterilluminate the disclosure and does not pose a limitation on the scope ofthe disclosure unless otherwise claimed.

FIG. 1 illustrates a schematic configuration and an optical arrangementof an optical device 100 according to an example embodiment, and FIG. 2illustrates a conceptual focusing operation of a geometric phase lensGPL that may be employed in the optical device 100 of FIG. 1.

The optical device 100 according to the example embodiment has a reducedchromatic aberration and focuses light of different wavelengths.

The optical device 100 includes a first backlight 110 outputting lightL1 of a first wavelength, a first lens 150 having a predetermined focallength with respect to the light L1 of the first wavelength emitted fromthe first backlight 110, a second backlight 120 outputting light L2 of asecond wavelength, a second lens 160 exhibiting different focal lengthswith respect to the light L1 of the first wavelength and the light L2 ofthe second wavelength, and a third backlight 130 outputting light L3 ofa third wavelength, and a third lens 170 exhibiting different focallengths with respect to the light L1 of the first wavelength, the lightL2 of the second wavelength, and the light L3 of the third wavelength.

The light L1 of the first wavelength, the light L2 of the secondwavelength, and the light L3 of the third wavelength are light in thewavelength range of visible light, and may be blue light, green light,and red light, respectively, but are not limited thereto.

The first backlight 110, the second backlight 120, and the thirdbacklight 130 are provided with a first emission surface 110 a, a secondemission surface 120 a, and a third emission surface 130 a respectivelythat emit light toward the first lens 150, the second lens 160, and thethird lens 170. The first backlight 110, the second backlight 120, andthe third backlight 130 are configured such that the first emissionsurface 110 a, the second lens 160, the second emission surface 120 a,the second lens 160, the third emission surface 130 a, and the thirdlens 170 are disposed in parallel with each other. An output coupler forlight emission may be formed on each of the first emission surface 110a, the second emission surface 120 a, and the third emission surface 130a.

As illustrated in FIG. 2, the first lens 150, the second lens 160, andthe third lens 170 may be the geometric phase lens GPL. The geometricphase lens GPL may be implemented in, for example, a liquid crystaldevice or a meta device, and may include a micro-patterned structure.The geometric phase lens GPL is designed to have a predeterminedrefractive power by modulating the phase of an incidence lightdifferently according to the position. For example, when light of aleft-handed circular polarization LCP is incident, the light may befocused with phase modulation to light of a right-handed circularpolarization RCP. However, embodiments are not limited thereto. Forexample, when the incident light is focused, the light of theright-handed circular polarization RCP may be modulated to the light ofthe left-handed circular polarization LCP, or the incidence light may bemodulated based on linear polarization. In addition, although a positiverefractive power is illustrated, the geometric phase lens GPL may bedesigned to exhibit negative refractive power, such as a concave lens.The geometric phase lens GPL may have a flat plate shape and implement adesired refractive power with a relatively small thickness.

However, because the geometric phase lens GPL adjusts a direction inwhich light travels through phase modulation, as illustrated in FIG. 2,the geometric phase lens GPL may show different focal lengths accordingto the wavelength of the incidence light. For example, the geometricphase lens GPL designed to have a first focal length f1 with respect tothe light L1 of the first wavelength exhibits a second focal length f2different from the first focal length f1 with respect to the light L2 ofthe second wavelength, and a third focal length f3 different from thefirst focal length f1 and the second focal length f2 with respect to thelight L3 of the third wavelength. A focal length may be inverselyproportional to the wavelength of the incidence light. For example, thegeometric phase lens GPL exhibits a focal length shorter than thedesigned focal length when light having a wavelength longer than thedesigned wavelength is incident, and a focal length longer than thedesigned focal length when light having a wavelength shorter than thedesigned wavelength is incident. The properties of the geometric phaselens GPL may be represented by chromatic aberration.

In the optical device 100 according to the example embodiment, detailsand arrangement positions of the first lens 150, the second lens 160,and the third lens 170 are set such that the light L1, L2, and L3 ofdifferent wavelengths may be focused on the same position.

The light L1 of the first wavelength is focused through the first lens150, the second lens 160, and the third lens 170, the light L2 of thesecond wavelength is focused through the second lens 160 and the thirdlens 170, and the light L3 of the third wavelength is focused throughthe third lens 170. According to such optical paths, the light L1, L2,and L3 of different wavelengths may be focused on substantially the samelocation, and chromatic aberration may be reduced or prevented.

A focal length of the first lens 150 with respect to the light L1 of thefirst wavelength may be f1_1, focal lengths of the second lens 160 withrespect to the light L1 of the first wavelength and the light L2 of thesecond wavelength may be f2_1 and f2_2, respectively, and focal lengthsof the third lens 170 with respect to the light L1 of the firstwavelength, the light L2 of the second wavelength, and the light L3 ofthe third wavelength may be f3_1, f3_2, and f3_3, respectively. Forexample, f2_1 and f2_2 may be different numerical values, and f3_1,f3_2, and f3_3 may also be different numerical values.

In the optical device 100 of the example embodiment, the first lens 150,the second lens 160, and the third lens 170 may be set such that theeffective focal length EFL (f1_1, f2_1, and f3_1) that is a combinationfocal length of f1_1, f2_1, and f3_1 and the EFL (f2_2, f3_2) that is acombination focal length of f2_2 and f3_2 are substantially the same asthe focal length f3_3 with respect to the light L3 of the thirdwavelength of the third lens 170.

A combination focal length EFL of two lenses having focal lengths f₁ andf₂ and a distance d between the centers may be obtained as shown inEquation 1.

$\begin{matrix}{{E\; F\; L} = \frac{f_{1}*f_{2}}{f_{1} + f_{2} - d}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

A combination focal length EFL of three lenses having the focal lengthsof f₁, f₂, and f₃ and distances d₁₂ and d₂₃ between the centers ofadjacent lenses may be obtained as shown in Equation 2.

$\begin{matrix}{{E\; F\; L} = \frac{\frac{f_{1}*f_{2}}{f_{1} + f_{2} - d_{12}}*f_{3}}{\frac{f_{1}*f_{2}}{f_{1} + f_{2} - d_{12}} + f_{3} - d_{23}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Considering the above equations and requirements that will be describedlater, details of the first lens 150, the second lens 160, and the thirdlens 170, that is, focal lengths with respect to light of differentwavelengths and arrangement spaces thereof may be set.

The first lens 150, the second lens 160, and the third lens 170 maysatisfy the following condition in Equation 3.EFL(f1_1,f2_1,f3_1)=EFL(f2_2,f3_2)=f3_3  [Equation 3]

However, embodiments are not limited thereto, and the difference betweenthe values may be set within a predetermined range such that the opticaldevice 100 has little chromatic aberration or a small value within adesired range.

For example, the first lens 150, the second lens 160, and the third lens170 may satisfy the following conditions in Equation 4 and Equation 5.|f3_3−EFL(f1_1,f2_1,f3_1)|/f3_3<0.0005  [Equation 4]|f3_3−EFL(f2_2,f3_2)|/f3_3<0.0005  [Equation 5]

FIG. 3 illustrates a schematic configuration and optical arrangement ofan optical device 101 according to another example embodiment.

The optical device 101 includes a first backlight 111, a first lens 150,a second backlight 121, a second lens 160, a third backlight 131 and athird lens 170.

The optical device 101 of the example embodiment is different from theoptical device 100 of FIG. 1 in that detailed configurations of thefirst backlight 111, the second backlight 121, and the third backlight131 are illustrated and the configurations of the first lens 150, thesecond lens 160, and the third lens 170 are substantially the same asthat of the optical device 100 of FIG. 1.

The first backlight 111 includes a first light source LS1 providing thelight L1 of the first wavelength, and a first light guide plate WG1guiding and emitting the light L1 of the first light source LS1 in adirection toward the first lens 150. The first light guide plate WG1includes a first input coupler 101 causing the light L1 of the firstlight source LS1 to be incident and a first output coupler OC1 emittingthe light L1 input through the first input coupler 101 toward the firstlens 150. Between the first light source LS1 and the first light guideplate WG1, a collimating lens 10 that collimates the light from thefirst light source LS1 such that the light is incident parallel to thefirst input coupler 101 is further disposed.

The first light source LS1 may be a coherent light source that emitscoherent light, and may be, for example, a laser diode (LD) or a lightemitting diode (LED).

The first light guide plate WG1 serves as an optical waveguidetransmitting light, and may include a material that is transparent tovisible light, such as glass, poly methyl methacrylate (PMMA), orpolydimethylsiloxane (PDMS). The first light guide plate WG1 includestwo surfaces 1 a and 1 b facing each other, and includes the first inputcoupler 101 for inducing the light incident from the first light sourceLS1 into the first light guide plate WG1 and the first output couplerOC1 for outputting light that is totally reflected from the two surfaces1 a and 1 b inside the first light guide plate WG1 and travels to theoutside of the first light guide plate WG1. For example, the first inputcoupler IC1 may be disposed on one edge of the surface 1 a of the firstlight guide plate WG1, and the first output coupler OC1 may be disposedon the other edge of the surface 1 a of the first light guide plate 120.

The first input coupler IC1 is configured to guide light incident on thefirst input coupler IC1 in a direction approximately normal to thesurface 1 a of the first light guide plate WG1 in an oblique direction.For example, the first input coupler 101 may be configured to guide thelight incident on the first input coupler 101 within a predeterminedangle of incidence with respect to a direction perpendicular to itssurface to the inside of the first light guide plate WG1. The lightguided to the inside of the first light guide plate WG1 is totallyreflected on the two surfaces 1 a and 1 b the first light guide plateWG1 that face each other repeatedly and travels along the inside of thefirst light guide plate WG1. The first output coupler OC1 is configuredto output light obliquely incident on the first output coupler OC1 in adirection approximately normal to the surface 1 a of the first lightguide plate WG1. The first output coupler OC1 may be configured to guideonly light incident within a predetermined range of an incidence angle,and not guide light incident at other ranges of angle. For example, thefirst output coupler OC1 may simply act as a transparent plate withrespect to light incident at an angle different from the set condition.

The first input coupler 101 and the first output coupler OC1 may beformed in a diffractive optical element (DOE) or a holographic opticalelement (HOE). The DOE may include a plurality of periodic fine gratingpatterns. The plurality of grating patterns of the DOE serves as adiffraction grating to diffract an incidence light. In particular,according to the size, height, period, etc. of the grating patterns, thetravel direction of the light may change by diffracting light incidentin a specific angle range and generating extinctive interference andconstructive interference. In addition, the HOE may include periodicfine patterns of materials with different refractive indices instead ofa grating pattern. The HOE merely differs from the DOE only in theconfiguration, and may have a same operation principle as an operatingprinciple of the DOE.

In the configuration of the first light guide plate WG1, the lightincident on the input coupler 101 is output to the outside of the lightguide plate 120 through the output coupler OC1. In addition, thedirectionality and coherence of light incident on the input coupler 101and output through the output coupler OC1 may be maintained within anangular range coupled by the input coupler 101.

Similarly, the second backlight 121 includes a second light source LS2providing the light L2 of the second wavelength and a second light guideplate WG2 guiding and emitting the light L2 of the second light sourceLS2 in a direction toward the second lens 160 and including a secondinput coupler 102 and a second output coupler OC2. In addition, acollimating lens 20 may be disposed between the second light source LS2and the second light guide plate WG2. The second output coupler OC2 mayact as a transparent plate with respect to the light L1 of the firstwavelength and emit the light L2 of the second wavelength in a directionnormal to the surface of the second light guide plate WG2.

In addition, the third backlight 131 includes a third light source LS3providing the light L3 of the third wavelength and a third light guideplate WG3 guiding and emitting the light L3 of the third light sourceLS3 in a direction toward the third lens 170 and including a third inputcoupler 103 and a third output coupler OC3. Also, a collimating lens 30may be disposed between the third light source LS3 and the third lightguide plate WG3. The third output coupler OC3 may act as a transparentplate with respect to the light L1 of the first wavelength and the lightL2 of the second wavelength, and emit the light L3 of the thirdwavelength in a direction normal to a surface of the third light guideplate WG3.

As described above, the light L1 of the first wavelength forms anoptical path in the order of the first output coupler OC1, the firstlens 150, the second output coupler OC2, the second lens 160, the thirdoutput coupler OC3, and the third lens 170. The light L2 of the secondwavelength forms an optical path in the order of the second outputcoupler OC2, the second lens 160, the third output coupler OC3, and thethird lens 170. The light L3 of the third wavelength forms an opticalpath in the order of the third output coupler OC3 and the third lens170. The light L1 of the first wavelength, the light L2 of the secondwavelength, and the light L3 of the third wavelength may be focused onthe same position with little or no chromatic aberration according tothe focal length requirements designed by the first lens 150, the secondlens 160, and the third lens 170 with respect to light of eachwavelength.

FIG. 4 illustrates a schematic configuration and optical arrangement ofan optical device 102 according to another example embodiment.

The optical device 102 of the example embodiment differs from theoptical device 101 of FIG. 3 in that the optical device 102 furtherincludes additional optical elements to control polarization of lightincident on the first lens 150, the second lens 160, and the third lens170.

As described above, the first lens 150, the second lens 160, and thethird lens 170, which are geometric phase lenses, may act on light of apredetermined polarization, and accordingly, the optical device 102 ofthe example embodiment further includes one or more phase retarders thatcause the light of the predetermined polarization to be incident on thefirst lens 150, the second lens 160, and the third lens 170.

The first lens 150, the second lens 160, and the third lens 170 mayfocus the light of the right-handed circular polarization RCP, and maychange the right-handed circular polarization RCP to the left-handedcircular polarization LOP. For this operation, a ¼ wave plate 40 may bedisposed between the first backlight 111 and the first lens 150, andfurther, a ¼ wave plate 50 may be disposed between the first lens 150and the second backlight 121. In addition, ¼ wave plates 60, 70, and 80may be disposed respectively between the second backlight 121 and thesecond lens 160, between the second lens 160 and the third backlight 131and between the third backlight 131 and the third lens 170.

The first backlight 111 may be configured to emit light of a linearpolarization, and the light L1 of the first wavelength emitted from thefirst backlight 111 passes through the ¼ wave plate 40 and changes inthe polarization state to the right-handed circular polarization RCP tobe incident on the first lens 150. The light L1 of the first wavelengthchanged to the left-handed circular polarization LCP and refractedaccording to a predetermined refractive power in the first lens 150passes through the ¼ wave plate 50 again and changes in the polarizationstate to linear polarization.

The light L1 of the first wavelength in the state of linear polarizationand the light L2 of the second wavelength in the state of linearpolarization emitted from the second backlight 121 pass through the ¼wavelength plate 60 and change to the state of the right-handed circularpolarization RCP to be incident on the second lens 160. Next, the lightL1 of the first wavelength and the light L2 of the second wavelengthpass through the second lens 160, are refracted according topredetermined certain refractive powers, and change to the state of theleft-handed circular polarization LOP. The light L1 of the firstwavelength in the state of linear polarization and the light L2 of thesecond wavelength in the state of the left-handed circular polarizationLCP pass through the ¼ wave plate 70 again, and change in thepolarization state to linear polarization.

The light L1 of the first wavelength and the light L2 of the secondwavelength in the state of linear polarization, and the light L3 of thethird wavelength in the state of linear polarization emitted from thethird backlight 131 pass through the ¼ wavelength plate 80 and change tothe state of the right-handed circular polarization RCP to be incidenton the third lens 170. Next, the light L1 of the first wavelength, thelight L2 of the second wavelength, and the light L3 of the thirdwavelength pass through the third lens 170, and are refracted accordingto predetermined certain refractive powers.

In the above description, the first lens 150, the second lens 160, andthe third lens 170 act on circular polarization and an additional phaseretarder is a ¼ wavelength plate, but embodiments are not limitedthereto. Depending on the polarization requirements of the first lens150, the second lens 160, and the third lens 170, other components maybe used or additional components may be added.

FIG. 5 illustrates a schematic configuration and optical arrangement ofan optical device 200 according to another example embodiment, and FIG.6 illustrates a conceptual optical operation of a diffraction-based beamdeflector BD that may be employed in the optical device 200 of FIG. 5.

The optical device 200 of the example embodiment is a beam deflectingdevice that exhibits reduced chromatic aberration and deflects light ofdifferent wavelengths.

The optical device 200 includes a first backlight 111 outputting thelight L1 of the first wavelength, a first beam deflector 250 deflectingthe light L1 of the first wavelength at a predetermined angle, a secondbacklight 121 outputting the light L2 of the second wavelength, a secondbeam deflector 260 deflecting the light L1 of the first wavelength andthe light L2 of the second wavelength at different angles, a thirdbacklight 131 outputting the light L3 of the third wavelength, and athird beam deflector 270 deflecting the light L1 of the firstwavelength, the light L2 of the second wavelength, and the light L3 ofthe third wavelength at different angles.

The first backlight 111, the second backlight 121, and the thirdbacklight 131 have the configurations described in the above-describedexample embodiments, and the first output coupler OC1, the first beamdeflector 250, the second output coupler OC2, the second beam deflector260, the third output coupler OC3, and the third beam deflector 270 aresequentially arranged in parallel with each other.

The first beam deflector 250, the second beam deflector 260, and thethird beam deflector 270 are diffraction-based beam deflectors BD asillustrated in FIG. 6. The beam deflector BD may be a diffractionelement including liquid crystal or an optical element that mayelectrically change phase. The beam deflector BD may be implemented in ageometric phase manner, or may be implemented as a meta elementincluding a micro-patterned structure. The beam deflector BD is designedto differently modulate the phase of the incidence light according tothe position to deflect the direction of the incidence light at apredetermined angle. Because such a method adjusts the direction inwhich light travels through phase modulation, as illustrated in FIG. 6,light may be deflected at different angles according to the wavelengthof incidence light. For example, the first beam deflector 250 designedto have a first deflection angle with respect to the light L1 of thefirst wavelength may exhibit a second deflection angle different fromthe first deflection angle with respect to the light L2 of the secondwavelength, and in addition, show a third deflection angle differentfrom the first deflection angle and the second deflection angle withrespect to the light L3 of the third wavelength. When light having awavelength different from a designed wavelength is incident on thediffraction-based beam deflector BD, the light may be deflected at adifferent angle from a designed deflection angle, which may berepresented by chromatic aberration.

In the optical device 200 according to the example embodiment, detailsand arrangement positions of the first beam deflector 250, the secondbeam deflector 260, and the third beam deflector 270 are set such thatthe light L1, L2, and L3 of different wavelengths may be deflected inthe same direction by the optical device 200.

The light L1 of the first wavelength is deflected at a predeterminedangle through each of the first beam deflector 250, the second beamdeflector 260, and the third beam deflector 270, the light L2 of thesecond wavelength is deflected through the second beam deflector 260 andthe third beam deflector 270, and the light L3 of the third wavelengthis deflected through the third beam deflector 270. According to suchoptical paths, the light L1, L2, and L3 of different wavelengths may bedeflected in substantially the same direction, and chromatic aberrationmay rarely appear.

An angle at which the first beam deflector 250 deflects the light L1 ofthe first wavelength may be a1_1, angles at which the second beamdeflector 260 deflects the light L1 of the first wavelength and thelight L2 of the second wavelength may be a2_1 and a2_2, respectively,and angles at which the third beam deflector 270 deflects the light L1of the first wavelength, the light L2 of the second wavelength, and thelight L3 of the third wavelength may be a3_1, a3_2, and a3_3,respectively. For example, a2_1 and a2_2 may be different numericalvalues, and a3_1, a3_2, and a3_3 may also be different numerical values.

The first beam deflector 250, the second beam deflector 260, and thethird beam deflector 270 may be also electrically controlled and mayadjust the direction in which light is deflected in detail. For example,the above numerical values can be adjusted in a predetermined range.

In the optical device 200 of the example embodiment, the first beamdeflector 250, the second beam deflector 260, and the third beamdeflector 270 may be set such that a combination deflection angleEDA(a1_1, a2_1, a3_1) of a1_1, a2_1, and a3_1 and a combinationdeflection angle EDA(a2_2, a3_2) of a2_2 and a3_2 are substantially thesame as the deflection angle a3_3 with respect to the light L3 of thethird wavelength of the third beam deflector 270.

The first beam deflector 250, the second beam deflector 260, and thethird beam deflector 270 may satisfy the following condition in Equation6.EDA(a1_1,a2_1,a3_1)=EDA(a2_2,a3_2)=a3_3  [Equation 6]

However, embodiments are not limited thereto, and the difference betweenthe values may be set within a predetermined range such that the opticaldevice 200 has little direction deviation depending on the wavelength ora small value within a desired range.

For example, the first beam deflector 250, the second beam deflector260, and the third beam deflector 270 may satisfy the followingconditions in Equation 7 and Equation 8.|a3_3−EDA(a1_1,a2_1,a3_1)|/a3_3<0.0005  [Equation 7]|a3_3−EDA(a2_2,a3_2)|/a3_3<0.0005  [Equation 8]

The above-described deflection angles are formed with the Z axis on theXZ plane, but are not limited thereto. The first beam deflector 250, thesecond beam deflector 260, and the third beam deflector 270 may be setsuch that the deflection angle may be set to be defined as an angleformed with Z in the YZ plane and may be defined on another plane.

FIG. 7 illustrates a schematic configuration and an optical arrangementof a display device 1000 according to an example embodiment.

The display device 1000 includes an optical device 1100 and a spatiallight modulator 1800.

The optical device 1100 may have low chromatic aberration and providelight focused on a predetermined position to the spatial light modulator1800, for example, and may have a configuration substantially the sameas or modified from the optical device 101 illustrated in FIG. 3.

The spatial light modulator 1800 modulates light from the firstbacklight 111, the second backlight 121, and the third backlight 131 ofthe optical device 1100 to generate a hologram image.

The spatial light modulator 1800 may form a hologram pattern accordingto a hologram data signal, for example, a computer generated hologram(CGH) signal, provided from a controller. After the light from the firstbacklight 111, the second backlight 121, and the third backlight 131 isincident on the spatial light modulator 1800 and is diffracted by thehologram pattern formed on the spatial light modulator 1800, aholographic image having a stereoscopic effect may be reproduced byextinctive interference and constructive interference. The spatial lightmodulator 1800 may use any of a phase modulator capable of performingonly phase modulation, an amplitude modulator capable of performing onlyamplitude modulation, and a complex modulator capable of performing bothphase modulation and amplitude modulation. As the spatial lightmodulator 1800, a liquid crystal on silicon (LCoS), a digitalmicromirror device (DMD), or a semiconductor modulator may be used.

In FIG. 7, the light passing through all of the first lens 150, thesecond lens 160, and the third lens 170 is incident on the spatial lightmodulator 1800, but embodiments are not limited thereto. For example,the positions of the third lens 170 and the spatial light modulator 1800may be switched.

In the display device 1000, the light focused on a predeterminedposition by the optical device 1100 without chromatic aberration isprovided to the spatial light modulator 1800, thereby providing anobserver with a good quality holographic image.

FIG. 8 illustrates a schematic configuration and an optical arrangementof a display device 1001 according to another example embodiment.

The display device 1001 of the example embodiment is different from thedisplay device 1000 of FIG. 7 in that the display device 1001 furtherincludes a beam deflector 1500 adjusting the position of a hologramimage.

The display device 1001 forms the hologram image on a predeterminedposition in an observer's view, and thus, the image may not berecognized when the position of the observer's eye changes from thepredetermined position. The beam deflector 1500 may vary a position atwhich the optical device 1100 focuses light on a focal plane FP. Theposition may be variable along the X direction on the focal plane FP,but is not limited thereto. For example, the position may be variablealong the Y direction and the beam deflector 1500 may be configured suchthat the position changes in a two-dimensional direction.

The beam deflector 1500 may be a liquid crystal deflector that diffractsincidence light to change a traveling direction of the incidence light.The beam deflector 1500 may be electrically controlled and adjust adirection in which light is deflected.

The display device 1001 may further include an eye tracking sensor inorder to obtain information necessary for varying the focusing position.The beam deflector 1500 may be controlled such that the position of theobserver's eye is determined by the eye tracking sensor and the light isfocused on the other position on the focal plane FP.

In FIG. 8, the third lens 170, the beam deflector 1500, and the spatiallight modulator 1800 are sequentially arranged, but embodiments are notlimited thereto, and the order of the three components may change. Forexample, the positions of the third lens 170 and the beam deflector 1500may be switched, and the positions of the third lens 170 and the spatiallight modulator 1800 may be switched.

Although the display devices 1000 and 1001 of FIGS. 7 and 8 illustrateoptical systems with respect to a single eye, these optical systems maybe provided for both eyes. The beam deflector 1500 provided in thedisplay device 1001 of FIG. 8 may be configured to divert light towardboth eyes.

FIG. 9 illustrates a schematic configuration and an optical arrangementof a display device 1002 according to another example embodiment.

The display device 1002 of the example embodiment is different from thedisplay device 1001 of FIG. 8 in that a beam deflector 1502 has aconfiguration in which light is diverted toward both eyes, and theremaining configuration is substantially the same.

The display device 1002 includes the optical device 1100 that providesfocusing light with little or no chromatic aberration, the beamdeflector 1502, and the spatial light modulator 1800. The display device1002 may further include an eye tracking sensor ES that senses theposition of observer's both eyes and a controller 1900 that controls thebeam deflector 1502 using information sensed by the eye tracking sensorES.

The beam deflector 1502 may be a liquid crystal deflector that diffractsincidence light to produce two light beams traveling at differentangles. The beam deflector 1502 may simultaneously and spatially divertlight toward the left and right eyes. The beam deflector 1502 maysequentially divert light toward the left and right eyes. The beamdeflector 1502 may be also electrically controlled and may adjust twodirections in which the light diverts in detail. The detailed positionchange of the left and right eyes may be sensed by the eye trackingsensor ES, and the position where the beam deflector 1502 diverges lightby utilizing the information sensed by the eye tracking sensor ES maychange two-dimensionally on the parallel focal plane FP in parallel withthe XY plane.

FIG. 10 illustrates a schematic configuration and an optical arrangementof a display device 1003 according to another example embodiment.

The display device 1003 of the example embodiment includes aconfiguration in which the optical devices 101 and 200 illustrated inFIGS. 3 and 5 are combined and the spatial light modulator 1800.

For example, the display device 1003 further includes the first beamdeflector 250, the second beam deflector 260, and the third beamdeflector 270 in addition to the display device 1000 illustrated in FIG.7.

The first beam deflector 250, the second beam deflector 260, and thethird beam deflector 270 may respectively adjust positions on whichlight is focused from the first backlight 111, the second backlight 121,and the third backlight 131 on the focal plane FP to reduce chromaticaberration. The first beam deflector 250 is disposed between the firstoutput coupler OC1 and the second output coupler OC2, the second beamdeflector 260 is disposed between the second the coupler OC2 and thethird output coupler OC3, and the third beam deflector 270 is disposedin a traveling path of the light from the third output coupler OC3.

In FIG. 10, although the first beam deflector 250 and the first lens 150are sequentially disposed between the first output coupler OC1 and thesecond output coupler OC2, the first lens 150 and the first beamdeflector 250 may be sequentially arranged between the first outputcoupler OC1 and the second output coupler OC2. similarly, the positionsof the second beam deflector 260 and the second lens 160 may beswitched, and the positions of the third beam deflector 270 and thethird lens 170 may be switched. In addition, the position of the spatiallight modulator 1800 may also be changed to between the third beamdeflector 270 and the third lens 170.

The first beam deflector 250, the second beam deflector 260, and thethird beam deflector 270 may be configured as described in FIG. 5 suchthat the light L1 of the first wavelength is sequentially deflected bythe first beam deflector 250, the second beam deflector 260 and thethird beam deflector 270, the light L2 of the second wavelength issequentially deflected by the second beam deflector 260 and the thirdbeam deflector 270, and the light L3 of the third wavelength isdeflected by the third beam deflector 270, and consequently thedeflection directions of the light L1 of the first wavelength, the lightL2 of the second wavelength, and the light L3 of the third wavelengthare substantially identical.

The first beam deflector 250, the second beam deflector 260, and thethird beam deflector 270 may also be electrically controlled and mayadjust the direction in which light is deflected in detail.

The display device 1003 may further include the eye tracking sensor ES,and the first beam deflector 250, the second beam deflector 260, and thethird beam deflector 270 may be controlled based on a signal sensed bythe eye tracking sensor ES. According to the operations of the firstbeam deflector 250, the second beam deflector 260, and the third beamdeflector 270, the position on which the light is focused may beadjusted two-dimensionally on the focal plane FP.

FIG. 11 illustrates a schematic configuration and an optical arrangementof a display device 1004 according to another example embodiment.

The display device 1004 includes an optical device 1200, a field lens1700, and the spatial light modulator 1800.

The optical device 1200 may provide directional light with little or nochromatic aberration, and may have a configuration substantially thesame as or modified from the optical device 200 described with referenceto FIG. 5.

The spatial light modulator 1800 modulates light from the optical device200 to generate a hologram image, and the field lens 1700 focuses thegenerated hologram image on a predetermined position. The positions ofthe field lens 1700 and the spatial light modulator 1800 may beswitched.

Although the display device 1004 is illustrated as an optical systemwith respect to a single eye, such an optical system may be provided forboth eyes. The first beam deflector 250, the second beam deflector 260,and the third beam deflector 270 provided in the optical device 1200 maybe configured to divert light toward both eyes.

FIG. 12 illustrates a schematic configuration and an optical arrangementof a display device 1004 according to another example embodiment.

The display device 1004 includes an optical device 1205 that may providedirectional light with little or no chromatic aberration, the field lens1700 and the spatial light modulator 1800. The display device 1004 mayfurther include the eye tracking sensor ES that senses the position ofobserver's both eyes and the controller 1900 that controlsdirectionality of light from the optical device 1205 by usinginformation sensed by the eye tracking sensor ES.

The display device 1004 according to the example embodiment is differentfrom the display device 1003 of FIG. 11 in that the first beam deflector250, the second beam deflector 260, and the third beam deflector 270 ofthe optical device 1200 provided in the display device 1003 of FIG. 11include the optical device 1205 configured to divert light toward botheyes.

The light from the optical device 1205 may be diverted toward both eyes,and the divergence direction may be adjusted according to the detailedposition of both eyes, and a direction adjustment with little deviationaccording to wavelengths is possible.

Although it is described that the above-described optical devices 100,101, 102, and 200 are applied to display devices, embodiments are notlimited thereto. For example, the above-described optical devices 100,101, 102, and 200 may be employed to various electronic devices in whichfocusing light or directional light with little deviation according tothe wavelengths may be utilized.

The above-described display devices 1000, 1001, 1002, 1003, 1004, and1005 may be applied to various types of wearable device displays such ashead mounted displays (HMDs), glasses-type displays, and goggle-typedisplays, etc.

The above-described display devices 1000, 1001, 1002, 1003, 1004, and1005 may also operate in conjunction with or connected to otherelectronic devices, such as a smart phone. For example, a controller ora processor driving the display devices 1000, 1001, 1002, 1003, 1004,and 1005 may be provided in smart phones, and the above-describeddisplay devices 1000, 1001, 1002, 1003, 1004, and 1005 may be providedin the smart phones.

The above-described optical device may minimize the deviation accordingto the wavelengths in controlling the direction of light of differentwavelengths.

The above-described optical device may be applied to a lens, a beamdeflector, etc., with little chromatic aberration, and may be applied toa display device that improves the image quality.

While the optical device and the display device including the opticaldevice have been shown and described with reference to the exampleembodiments illustrated in the drawings, it will be understood by thoseof ordinary skill in the art that various changes in form and detailsmay be made therein without departing from the spirit and scope asdefined by the following claims. It should be understood that exampleembodiments described herein should be considered in a descriptive senseonly and not for purposes of limitation. Descriptions of features oraspects within each example embodiment should typically be considered asavailable for other similar features or aspects in other embodiments.

What is claimed is:
 1. An optical device comprising: a first backlightconfigured to output first light of a first wavelength, the firstbacklight comprising a first light source configured to emit the firstlight, and a first light guide plate comprising a first input coupler onwhich the first light from the first light source is incident and afirst output coupler through which the first light output; a first lensdisposed to face the first output coupler and having a refractive powerwith a focal length of f1_1 with respect to the first light of the firstwavelength; a second backlight configured to output second light of asecond wavelength, the second backlight comprising a second light sourceconfigured to emit the second light, and a second light guide platecomprising a second input coupler on which the second light from thesecond light source is incident and a second output coupler throughwhich the second light output, the second output coupler being disposedin parallel to the first output coupler; a second lens disposed to facethe second output coupler and having a refractive power with differentfocal lengths of f2_1 and f2_2 with respect to the first light of thefirst wavelength and the second light of the second wavelength,respectively; a third backlight configured to output third light of athird wavelength, the third backlight comprising a third light sourceconfigured to emit the third light, and a third light guide platecomprising a third input coupler on which the third light from the thirdlight source is incident and a third output coupler through which thethird light output, the third output coupler being disposed in parallelto the first output coupler; and a third lens disposed to face the thirdoutput coupler and having refractive power with different focal lengthsof f3_1, f3_2 and f3_3 with respect to the first light of the firstwavelength, the second light of the second wavelength, and the thirdlight of the third wavelength, respectively.
 2. The optical device ofclaim 1, wherein the first lens, the second lens, and the third lens aregeometric phase lenses.
 3. The optical device of claim 1, wherein afocal length of the first lens with respect to the first light of thefirst wavelength is f1_1, focal lengths of the second lens with respectto the first light of the first wavelength and the second light of thesecond wavelength are f2_1 and f2_2, respectively, and focal lengths ofthe third lens with respect to the first light of the first wavelength,the second light of the second wavelength, and the third light of thethird wavelength are f3_1, f3_2, and f3_3, respectively, and EFL (f1_1,f2_1, and f3_1) that is a combination focal length of f1_1, f2_1, andf3_1 satisfies the following condition:|f3_3−EFL(f1_1,f2_1,f3_1)|/f3_3<0.0005.
 4. The optical device of claim3, wherein EFL(f2_2, f3_2) that is a combination focal length of f2_2and f3_2 satisfies the following condition:|f3_3−EFL(f2_2,f3_2)|/f3_3<0.0005.
 5. The optical device of claim 1,wherein the first lens, the second lens, and the third lens operate withrespect to light of a predetermined polarization, and the optical devicefurther comprises at least one phase retarder configured to causeincident light of the predetermined polarization to be incident on thefirst lens, the second lens, and the third lens.
 6. An optical devicecomprising: a first backlight configured to output first light of afirst wavelength, the first backlight comprising a first light sourceconfigured to emit the first light, and a first light guide platecomprising a first input coupler on which the first light from the firstlight source is incident and a first output coupler through which thefirst light output; a first beam deflector disposed to face the firstoutput coupler and configured to deflect the first light of the firstwavelength at a predetermined angle of a1_1; a second backlightconfigured to output second light of a second wavelength, the secondbacklight comprising a second light source configured to emit the secondlight, and a second light guide plate comprising a second input coupleron which the second light from the second light source is incident and asecond output coupler through which the second light output, the secondoutput coupler being disposed in parallel to the first output coupler; asecond beam deflector disposed to face the second output coupler, thesecond output coupler being configured to deflect the first light of thefirst wavelength and the second light of the second wavelength atdifferent angles of a2_1 and a2_2, respectively; a third backlightconfigured to output third light of a third wavelength, the thirdbacklight comprising a third light source configured to emit the thirdlight, and a third light guide plate comprising a third input coupler onwhich the third light from the third light source is incident and athird output coupler through which the third light output, the thirdoutput coupler being disposed in parallel to the first output coupler;and a third beam deflector disposed to face the third output coupler,the third beam deflector being configured to deflect the first light ofthe first wavelength, the second light of the second wavelength, and thethird light of the third wavelength at different angles of a3_1, a3_2,and a3_3, respectively.
 7. The optical device of claim 6, wherein thefirst beam deflector, the second beam deflector, and the third beamdeflector are diffraction-based deflectors.
 8. The optical device ofclaim 6, wherein an angle at which the first beam deflector deflects thefirst light of the first wavelength is a1_1, angles at which the secondbeam deflector deflects the first light of the first wavelength and thesecond light of the second wavelength are a2_1 and a2_2, respectively,and angles at which the third beam deflector deflects the first light ofthe first wavelength, the second light of the second wavelength, and thethird light of the third wavelength are a3_1, a3_2, and a3_3,respectively, and EDA(a1_1, a2_1, a3_1) that is a combination deflectionangle of a1_1, a2_1, and a3_1 satisfies the following condition:|a3_3−EDA(a1_1,a2_1,a3_1)|/a3_3<0.0005.
 9. The optical device of claim8, wherein EDA(a2_2, a3_2) that is a combination deflection angle ofa2_2 and a3_2 satisfies the following condition:|a3_3−EDA(a2_2,a3_2)|/a3_3<0.0005.
 10. A display device comprising: theoptical device of claim 1; and a spatial light modulator configured togenerate a hologram image by modulating the first light output from thefirst backlight, the second light output from the second backlight, andthird light output from the third backlight.
 11. The display device ofclaim 10, wherein the first lens, the second lens, and the third lensare geometric phase lenses.
 12. The display device of claim 10, whereina focal length of the first lens with respect to the first light of thefirst wavelength is f1_1, focal lengths of the second lens with respectto the first light of the first wavelength and the second light of thesecond wavelength are f2_1 and f2_2, respectively, and focal lengths ofthe third lens with respect to the first light of the first wavelength,the second light of the second wavelength, and the third light of thethird wavelength are f3_1, f3_2, and f3_3, respectively, and EFL (f1_1,f2_1, and f3_1) that is a combination focal length of f1_1, f2_1, andf3_1 satisfies the following condition:|f3_3−EFL(f1_1,f2_1,f3_1)|/f3_3<0.0005.
 13. The display device of claim12, wherein EFL(f2_2, f3_2) that is a combination focal length of f2_2and f3_2 satisfies the following condition:|f3_3−EFL(f2_2,f3_2)|/f3_3<0.0005.
 14. The display device of claim 10,further comprising a beam deflector configured to adjust a position ofthe hologram image generated by the spatial light modulator.
 15. Thedisplay device of claim 10, further comprising: a first beam deflectordisposed between the first output coupler and the second output coupler,the first beam deflector being configured to deflect the first light ofthe first wavelength at a predetermined angle; a second beam deflectordisposed between the second output coupler and the third output coupler,the second beam deflector being configured to deflect the first light ofthe first wavelength and the second light of the second wavelength atdifferent angles; and a third beam deflector disposed such that thefirst light, the second light, and the third light output from the thirdoutput coupler is incident on the third beam deflector, the third beamdeflector being configured to deflect the first light of the firstwavelength, the second light of the second wavelength, and the thirdlight of the third wavelength at different angles.
 16. The displaydevice of claim 15, wherein the first beam deflector, the second beamdeflector, and the third beam deflector are diffraction-baseddeflectors.
 17. The display device of claim 15, wherein an angle atwhich the first beam deflector deflects the first light of the firstwavelength is a1_1, angles at which the second beam deflector deflectsthe first light of the first wavelength and the second light of thesecond wavelength are a2_1 and a2_2, respectively, and angles at whichthe third beam deflector deflects the first light of the firstwavelength, the second light of the second wavelength, and the thirdlight of the third wavelength are a3_1, a3_2, and a3_3, respectively,and EDA(a1_1, a2_1, a3_1) that is a combination deflection angle ofa1_1, a2_1, and a3_1 satisfies the following condition:|a3_3−EDA(a1_1,a2_1,a3_1)|/a3_3<0.0005.
 18. The display device of claim17, wherein EDA(a2_2, a3_2) that is a combination deflection angle ofa2_2 and a3_2 satisfies the following condition:|a3_3−EDA(a2_2,a3_2)|/a3_3<0.0005.
 19. The display device of claim 15,wherein the first beam deflector, the second beam deflector, and thethird beam deflector are electrically controlled to adjust a directionin which incident light is deflected.
 20. The display device of claim19, further comprising an eye tracking sensor, wherein the first beamdeflector, the second beam deflector, and the third beam deflector arecontrolled based on a signal sensed by the eye tracking sensor.
 21. Adisplay device comprising: the optical device of claim 6; a spatiallight modulator configured to generate a hologram image by modulatingthe first light of the first wavelength output from the first backlight,the second light of the second wavelength output from the secondbacklight, and the third light of the third wavelength output from thethird backlight; and a field lens configured to focus the hologram imagegenerated by the spatial light modulator at a predetermined position.22. The display device of claim 21, wherein the first beam deflector,the second beam deflector, and the third beam deflector are electricallycontrolled to adjust a direction in which incident light is deflected.23. The display device of claim 22, further comprising an eye trackingsensor, wherein the first beam deflector, the second beam deflector, andthe third beam deflector are controlled based on a signal sensed by theeye tracking sensor.